The present invention relates to a fountain assembly for applying a fluid composition such as ink, uniformly to the circumferential surface of a rotating transfer roller, for example, in a flexographic printing apparatus.
It is well known in the art to apply a liquid substance to a moving web of material. In particular, in the art of printing, ink must be moved from a storage reservoir to a series of ink transfer rollers by means of an ink fountain. In the technique of flexographic printing, it is known to apply colored inks to a web of a moving substrate, such as paper, with a rotating transfer or anilox roller, and to directly apply the ink uniformly and in a metered amount onto such a roller by means of an ink fountain assembly. From the roller, the ink is transferred to a plate cylinder and then to the material to be printed. Fountain assemblies generally include a channel extending the length of the transfer roller and in contact with the circumferential surface of it. A regulated amount of ink is continuously supplied to the fountain and then from the fountain to the roller with excess ink being returned from the fountain to an ink storage reservoir. A pair of doctor blades extend longitudinally on either side of the channel. The doctor blades are angled toward the transfer roller surface and serve both to seal the channel to the roller and to form an uniform film of the coating liquid on the roller transfer surface. As the roller rotates with respect to the fountain, microscopic cells engraved on the roller fill with ink. The doctor blades scrape excess ink from the roller and leave a uniform film of ink across the roller. The blades acts as an ink seal between the fountain body and the roller. The assembly also has some means to seal the channel at its ends so that the ink does not escape from the sides of the fountain assembly. This type of coating system is particularly used in flexographic and gravure printing, and coating applicators in a variety of industrial processes.
Fountain assemblies in and of themselves are known in the art. U.S. Pat. Nos. 4,026,210 and 5,027,513 disclose a printing apparatus having a doctor blade made from steel and teflon polymer. U.S. Pat. Nos. 4,821,672; 5,125,341 and 4,590,855 disclose the various types of end seals useful in fountain assemblies. U.S. Pat. No. 5,003,877 discloses an inker having dams that confine ink to a specific area of the rollers and water is used as a lubricating fluid. U.S. Pat. No. 3,186,339 shows an apparatus where fluid under pressure is used to move a number of plungers which cause a doctor blade to be pressed against a roller. U.S. Pat. No. 4,463,675 shows an apparatus which uses fluid pressure applied to a number of cylinders to press a blade against a roller. U.S. Pat. Nos. 4,906,335 and 4,789,432 teach fluid pressure application means that is actuated to press a blade against a roller and liquid filled tubes are used to effect angular adjustment. U.S. Pat. No. 4,461,211 shows fluid pressure means to press an inking assembly including blades against a roller. U.S. Pat. No. 5,003,877 discloses a pumped ink supply and a water wash that cleans the inker. Wash fluid is conducted through the ink supply lines rather than through nozzles in the doctor blade assembly. U.S. Pat. Nos. 5,085,144 and 5,058,502 show supplying ink to fountains. U.S. Pat. No. 5,040,457 discloses spray nozzle assemblies with press dampeners for use during offset printing, but which are not used to clean fountain assemblies. U.S. Pat. No. 4,796,528 shows an ink fountain with zone separators to permit use of different inks simultaneously.
An important factor for effective doctoring is to maintain doctor blade control. That is to keep the blades at a uniform blade angle and pressure along their entire length at a contact line with the rotating transfer cylinder. If the blade angle is incorrect, wiping action, and thus printing will be poor. Excessive blade loading pressure will also accelerate wear of both the blade and the roller surface and increase friction which will cause premature roller wear. One reason for difficulty with doctor blade control is that the fountain assembly has considerable mass since it is manufactured from a block of metal, usually cast aluminum with an electroless nickel coating for corrosion resistance. In one aspect of the present invention, this problem is solved by producing a fountain assembly which is composed of light weight, polymeric, plastic materials which are much easier to control than solid metal assemblies. The weight of the fountain of the present invention typically has only one-third of the weight of prior art fountains. However, lightness of weight of assembly material has the disadvantage of loss of rigidity of the blade assembly. This produces a deflection of the fountain thus causing the blades to have a tendency to be uneven across the length of the roller surface. This flexibility problem is solved without sacrificing lightness of weight by providing a fountain with a rigid metal backbone. An important additional feature of the invention is that the fountain assembly can be adjusted by hand without the use of separate tools. Prior art fountains are complex to adjust, and hence industrial establishments are induced to have spare fountains on hand for substitution onto coating machines. In effect, the spare fountains are adjusted off the coating machine and then subsequently attached to the coater. This substitution causes excessive down time as well as a high cost in extra fountains. Additionally, loose tools are easily lost. In contrast, the tool-less fountain of this invention is adjustable by hand without separate tools. This allows quick make-ready of the fountain by simple adjustment while it is still attached to the coating machine. Production time loss is thus minimized. The resulting fountain assembly is light weight, rigid, corrosion resistant, and easily cleaned and maintained without the use of tools. The invention provides an improved fountain assembly whose additional improved features are discussed hereinafter.